Resistor grid and method of making



May 19, 1959 A. w. FRANKLIN 2,886,854

RESISTOR GRID AND METHOD OF MAKING Filed Jan. '7. 1955 I N VEN TOR AA5587 WfiPAA KA //v Arm/Wm:

United States Patent'O RESISTOR GRID AND METHOD OF MAKING Albert W.Franklin, Mount Vernon, NY.

Application January 7, 1955, Serial No. 480,343

1 Claim. (Cl. 18-59) This invention comprises a novel form of resistoror resistor grid and methods by means of which it may be manufactured.

An object of this invention is to produce a resistor assembly comprisingone or more separate resistors or groups of resistors for providing insome forms a unitary resistor grid having a substantial part or all ofthe required individual resistor elements for a complex electricalcircuit.

Another object of the invention is to provide novel methods ofmanufacturing such resistor grids including as refinements proceduresfor controlling the unit resistivity of the individual resistors withinclose tolerances and conversely providing means for varying the unitresistivity to provide resistors of difierent values or resistors of thesame value within narrow resistance tolerances.

One object of the invention is to provide novel methods of manufacturingresistors and resistor assemblies employing an insulating supporttherefor as a mold during the process of forming the resistors, whichmold becomes a part of the final product.

Still another object of the invention is to provide resistors made ofmolded resistance powders and powder mixtures in which the insulatingsupport therefor forms a substantially protective housing for theresistors molded from such powders and powder mixtures.

Still another object of the invention is to provide a novel method ofincorporating the conductive contacts or connectors for the resistances.

Still another object of the invention is to form a novel type ofresistor or resistor grid consisting of an insulating support andhousing, the resistor elements per se, the terminal contacts thereforand the attachments for securing the parts together into a finishedunit.

Other and more detailed objects of the invention will be apparent fromthe following description of the em bodiments of the inventionillustrated in the attached drawings.

In the drawings,

Figure 1 is a plan view of a resistor grid in accordance with thisinvention comprising three subdivisions each composed of a plurality ofindividual resistors of difierent resistance values;

Figure 2 is a cross-sectional view taken on the line 22 of Figure 1;

Figure 3 is a cross-sectional view taken on the line 33 of Figure 1;

Figure 4 is a longitudinal, vertical, cross-sectional view through aresistor assembly in the process of fabrication in accordance with thisinvention, showing the die members by means of which the resistanceelements are formed in and secured in the insulating support;

Figure 5 is a perspective view of a portion of the insulating support.

Basically the resistor assembly of this invention consists of aninsulating support having a plurality of suit- "Ti a ably shapedapertures therethrough or recesses formed therein in which resistancepowders or powder mixtures of suitable characteristics are compressedand formed and secured. The apertures or recesses are previouslyprovided with terminal contacts, as will be explained in detail, so thatwhen under pressure the resistance powder or powder mixtures have beenfinally formed terminal connections therefor will be automaticallyprovided. An important feature of this invention is the use of theinsulating support as the primary mold into which the resistance powderor powder mixtures are compressed for final formation and lockingtherein.

Referring to the drawings, the insulating support illus trated consistsof a flat sheet of insulating or block material of the necessarycharacteristics, and of any required configuration. For example, asillustrated, the insulating support 10 can consist of a rectangular bodyof insulating material having the necessary electrical and mechanicalcharacteristics for the job at hand, including sufiicient form retainingcharacteristics under the forces of the processing, so as not to bedistorted thereby.

Various forms of natural and synthetic materials can be used for thissupport, of which there are many commercially available. By way ofexample, the insulating support 10 can be made of Bakelite, Masonite,nylon, fiberboard, and in fact any of the many available modern plasticcompositions. The board 10 is provided with one or more apertures orrecesses 12 which can be either punched in the support or formed bymolding to suitable form and dimensions. It will be understood that theopenings 12 can be apertures extending all the Way through the support10, or they may be channels, closed on one side. Their cross-sectionalconfiguration is not important, but the rectangular form is apparentlydesirable. It is to be noted that the crosssectional dimensions of theopenings 12 can be uniform or varied and/or their lengths may be varied,all as illustrated in the drawings.

Attached to the support 10 at the end of each of the apertures 12 is ametal contact 16 shown in this case in the form of an L-shaped metalpiece dimensioned so that one arm thereof will overlie one end of theassociated recess and the other arm will overlie the adjacent face ofthe support 10. These terminal contacts 16 are secured in place in anysuitable manner, as for example by means of the eyelets 18. The terminalconnectors at the opposite ends of the openings 12 can take many formscomprising, for example, individual terminal pieces similar to theterminal 16 or of the form illustrated at 20, 22 and 24. The terminal 20comprises a metal strip as shown, having a plurality of right angledextensions or arms longitudinally spaced so as to fit accurately in theends of the apertures 12 and the group interconnected thereby.

As shown in Figure 3, the connector terminal 20 consists of a continuousstrip of metal which overlies one face of the support 10 and has aseries of spaced fingers which extend into the adjacent ends of theopenings 12. The terminal 20 is secured to the support 10, as forexample by means of eyelets 18. As illustrated in Figure 1, the completeassembly has three sub-resistor assemblies determined by the size of theterminal connectors 20, 22 and 24. Within the openings 12 is formedunder pressure a series of individual resistors 26 by filling them witha resistance powder or powder mixture which when compressed will havethe required unit resistivity to provide resistors 26 each of thedesired individual resistance value. After compression the loose mixtureor powder becomes a coalesced form sustaining body which is held in theopenings 12 as a result of the respect to the slots containing resistors26 and 26 binding pressures produced as the powders are compressed toform the resistance bodies.

There are many forms and types of resistance powders and powder mixturessuitable for this purpose now commercially available and further detailswith respect thereto are unnecessary. As will be appreciated fromexamining the drawings, the terminal members are attached to theinsulating support after the spaces 12 have been formed in the supportand before the insulating powder is filled thereinto.

As'suggested above, the support forms the mold for the powders. It isplaced in a cavity in a die body 36, which cavity snugly fits thesupport to brace it against substantial distortion under the pressuresinvolved. The powders are then filled into the spaces 12 and a die 28,of any suitable form of power operated ram, is moved down to compressthe powders. As will be appreciated the die 28 is provided with activedie projections 30 which are sized and positioned so as to enter theopenings 12 and form a ram to compress'the powders. Since it is anadvantage of this method that even with the same powder mixtures variousresistance characteristics can be imparted to the resistors 26 byvarying the pressure thereon 'as Well as by varying the dimensions ofthe spaces 12, it follows that as illustrated at 32 and 34 the male diemembers can have different lengths. Thus the die member 32 is longerthan the die members 30, so that it will compress the powder in theassociated cavity to a greater degree to provide a resistor 26 ofgreater compactness and less height than the resistors 26. Converselythe male die 34 is shorter than the die members 30, so that it does notcompress the powder forming the resistor 26 as much as in the case ofresistors 26. It will be understood, of course, that this will havemarked and measured eflr'ects on the unit resistivity of the variousresistors.

It follows as a natural development of this thought that some or all ofthe male die members 30,for example as in the case of the die members 32and 34, may be made adjustable in a vertical direction, Figure 4. Thiscan be accomplished in various ways, as for example in the case of themale die members 32 and 34 the ram or pressure member 28 can be providedwith grooves into which the interchangeable male die members may bemounted. To illustrate this, for example, the male die member 32 can beinterchanged with the male die member 34, switching the efiects whichthey produce with It is also possible with this arrangement to use maledie members of varying lengths to accommodate openings 12 of diflerentlengths. These and other similar variations are contemplated as beingwithin the scope of this invention.

For example, it is possible, as indicated at 26 to in some cases formprojections on the die body 36, reducing the depth of the openings 12 atsuch points any desired amount so that the resistor 26 will be of stillless vertical height if conditions dictate. The projections 36 could beinterchangeable just as could the male die members.

As a result of these variations it will be seen that the amount ofcompression, the vertical height, and the spacing of the top and bottomsets of resistors, can be varied over a wide range with resultantchanges in mechanical and electrical properties. At this point it is tobe noted that as suggested above the openings 12 instead of beingapertures all the way through the support, could be closed on one side,and if in cases where the resistors are to be completely enclosed, thespaces at the top and/or bottom faces of the resistors can be filled inflush with the faces of the insulating support 10 to form a moisture andotherwise protected and fully or partially enclosed unit.

It is noted, although now clear, that when the powders are molded intofinal dimensions the resulting resistors are brought into electrical andmechanical contact at their respective ends with the contact terminals16, 20, 22 and 24.

It is within the scope of this invention in some forms to premold theresistor powders into resistance units 26, which may then be inserted inthe slots or recesses 12, as form sustaining units which could becemented or otherwise secured in place.

It is made amply clear from the above that the sub ject matter of thisinvention is capable of considerable variations in details, and I donot, .therefore, wish to be strictly limited to the illustrative exampleherein disclosed, but only as required by the appended claim.

What is claimed is:

A method as disclosed comprising the steps of positioning an insulatingsupport with openings on a fixed platform, filling a quantity ofresistance powder in said openings and simultaneously subjecting saidpowder in said openings to different amounts of pressure to form acoalesced form-sustaining resistor body having different resistancevalues.

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